I'm almost sure that the "lite" version was the result of the development team failing to get the game ready on time, hence the weird workarounds (such as having other, small items act as heavy rocks), the slow screen updates, and that unfortunate bug that allowed you, one screen before the end sequence, to jump off the map and into an inescapable limbo of messy test graphic screens. Deeply frustrating, and a clear sign of inadequate playtesting.

It also looks very much as if C64 Spellbound was an attempt to completely rewrite the game engine for C64, with a distinctly different main sprite, background tileset, and transparency effects on Dizzy and the text panels. Possibly writing the engine caused delays, and they had to release the lite game as a stopgap while working on the full version (and even that was lacking many features from the Spectrum version).

Thought the Lite version (when it was re-released) was a nice little game, showed how good the Lite version can be if programmed properly. On it's original release back in 1991 I hated it because of the slow screen updates, the transparent text blocks which made reading long conversations very difficult, and what the heck was wrong with the windy shaft in the original C64 Lite version? It took an eternity to float up it. Glad the re-makers took more time and care over it.